We only use "से" with other words like "से अच्छा", "से बड़ा", "से छोटा" and "से बेहतर" when we are talking about comparison as in english when the word ''than'' is included in the sentence. One more thing the word "बेहतर" becomes "बेहतरीन" when we are praising someone's qualities like "वह एक बेहतरीन खिलाड़ी है।" (He is a great player)
से means 'than' in this context Better than him or better than you or better than me or better than this/that needs 'से बहतर' When there is no direct comparison specified, for example 'this book is better' It will be 'यह किताब बहतर है'
If you instead write, 'यह किताब से बहतर है' it will became 'This is better than book'
If the sentence has a 'than' you add the से